Hexavalent chromium detector

ABSTRACT

The present invention relates to a molecular-based system for the optical detection, quantification and detoxification of hexavalent chromium (Cr 6+ ) by reversible metal-substrate electron transfer. More particularly, the invention provides a Cr 6+  sensor device comprising a divalent osmium (Os 2+ )-, iron (Fe 2+ )- or ruthenium (R 2+ )-based pyridyl complex capable of changing its oxidation state in response to a reduction of Cr 6+  at the presence of H + , thereby causing a reversible and optically readable change in optical properties of said complex. The Os 2+ -, Fe 2+ - or R 2+ -based pyridyl complex used according to the invention can be used for selective detection and quantification of Cr 6+ , as well as for catalytic detoxification of Cr 6+ .

TECHNICAL FIELD

The present invention relates to a molecular-based system, moreparticularly, to a divalent osmium-, iron- or ruthenium-based pyridylcomplex, for the optical detection, quantification and detoxification ofCr⁶⁺ by reversible metal-substrate electron transfer.

BACKGROUND ART

The most remarkable occurrence of chromium in nature is found in rubyand emerald gemstones, where replacing Al³⁺ by Cr³⁺ produces thecharacteristic red and green colors of the ruby and emerald gemstones,respectively. Chromium exists in oxidation states ranging fromCr²⁺-Cr⁶⁺, wherein Cr³⁺ is thermodynamically the most stable and alsothe most important, being an essential trace element with a daily uptakeof approximately 25-50 μg. However, in the higher oxidation states,e.g., as Cr⁶⁺, it is extremely dangerous being 500-1000 times more toxicthan Cr³⁺. Long term exposure to Cr⁶⁺ can lead to lung cancer, chronicbronchitis, asthma, emphysema, pulmonary fibrosis and other kinds ofdiseases (Reynolds et al., 2007; Zhitkovich, 2005; Levina and Lay,2005). According to the US Department of Health and Human Services, themaximum exposure limit in air varies between 0.5-100 μg/m³, whereas inwater the maximum exposure limit is 100 μg/l (ATSDR Chromium Toxicity,US Department of Health and Human Services, 2000).

The main sources for Cr⁶⁺ are modern chemical and industrial processesincluding oil and coal combustion, manufacturing of textile dyes,fabrication of nuclear weapons, chrome plating, metal finishing, andleather and wood preservation. These processes create a vast amount oftoxic waste (Singh and Gupta, 2007; Liu et al., 2006; Gheju and Iovi,2006; Mytych and Stasicka, 2004; Kieber et al., 2002). For example, theUnited States annually emits tons of Cr⁶⁺ as atmospheric pollution.Besides that, there is additional pollution of Cr⁶⁺ as waste water(ATSDR Chromium Toxicity, US Department of Health and Human Services,2000). Therefore, selective detection and quantification, together withdetoxification of Cr⁶⁺, are of high importance.

Current detoxification of Cr⁶⁺ is based on chemical reduction withstoichiometric amounts of iron(sulfur) salts followed by precipitationwith a base (Eary and Rai, 1988; EPA, 1980, 2000). Although severalsophisticated techniques are available to detect and quantify Cr⁶⁺(Marqués et al., 2000), a selective and cost-effective sensor systemwith minimum requirements for sample preparation is highly desirable.Alternative approaches are rare (Boiadjiev et al., 2005; Tian et al.,2005; Turyan and Mandler, 1997; Ji et al., 2001). Cr⁶⁺ undergoesreduction in solution in the presence of H⁺ and low-valent metal centerssuch as Fe²⁺, Mn²⁺, V³⁺ or Os²⁺ (Espenson, 1970; Davies and Espenson,1970; Birk, 1969; Westheimer, 1949). For example, [Os(bpy)₃]Cl₂ reactswith K₂Cr₂O₇ in water under acidic conditions (pH=1) to afford Cr³⁺, asmay be indicated by electron spin resonance (ESR) spectroscopy.Monolayer chemistry is rapidly developing (Collman et al., 2007;Yerushalmi et al., 2004; Liu et al., 2003; Lahann et al., 2003; Guptaand van der Boom, 2006, 2007; Gupta et al., 2006, 2007; Baker et al.,2006; Gulino et al., 2005; Basabe-Desmonts et al., 2004; Ashkenasy etal., 2000; Crooks and Ricco, 1998), and such, well-designed interfaceshave been used to detect various analytes (Gupta and van der Boom, 2006,2007; Gupta et al., 2006, 2007; Baker et al., 2006; Gulino et al., 2005;Basabe-Desmonts et al., 2004; Ashkenasy et al., 2000; Crooks and Ricco,1998). However, the design of a suitable platform for detecting specificmetal ions in a matrix remains a challenging task (Gupta and van derBoom, 2007; Zhang et al., 2006).

International Publication No. WO 2006085319 and the corresponding USPublication No. 20070258147, herewith incorporated by reference in theirentirety as if fully disclosed herein, disclose a device havingreversibly changeable and optically readable optical properties, thedevice comprising a substrate having an electrically conductive surfaceand carrying a redox-active layer structure configured to have at leastone predetermined electronic property including at least one ofelectrodensity and oxidation state, said at least one electronicproperty being changeable by subjecting the layer structure to anelectric field, wherein the electronic property of the layer structuredefines an optical property of the structure thereby determining anoptical response of the structure to certain incident light, the deviceenabling to effect a change in said electronic property that results ina detectable change in the optical response of the layer structure.

The aforesaid US 20070258147 further discloses a sensor deviceconfigured and operable for sensing at least one predetermined cation,anion, radical, liquid or gas substance, the device comprising aredox-active layer structure selected to be capable of changing itsoxidation state in response to a reaction with said at least onesubstance, thereby causing a change in optical properties of saidstructure, said change being reversible and being optically readable. Asdefined in the aforesaid US publication, the cation to be recognizedsaid sensor device may be selected from the group consisting of[Ru(phen)₃]³⁺, [Ru(bipy)₃]³⁺, [trianthrene]⁺, [Fe(bipy)₃]³⁺, Pu⁴⁺, Au⁺,Ag²⁺, Ag⁺, Ce⁴⁺, Ru³⁺, Ir³⁺, Ir⁴⁺, Rh⁺, Rh²⁺, U²⁺, U³⁺, U⁴⁺, U⁵⁺, Rh³⁺,Pd²⁺, Pd⁴⁺, Pt²⁺, Pt⁴⁺, Ni²⁺, Ni⁴⁺, Co³⁺, Hg²⁺, Cu²⁺, Cu⁺, Cd²⁺, Pb²⁺,Pb⁴⁺, Sn²⁺, Sn⁴⁺, W⁺, NO⁺, Fe²⁺, Fe³⁺, an actinide and a lanthanidecation. In a particular embodiment, the redox-active layer structure ofsaid sensor device comprises the osmium polypyridyl compoundbis(2,2′-bipyridine)[4′-methyl-4-(2-(4-(3-propyltrimethoxysilane)pyridinium)ethenyl)-2,2′-bipyridine]osmium(II)[tris(hexafluorophosphate)/tri-iodide],respectively.

SUMMARY OF INVENTION

It has been found, in accordance with the present invention, thatdivalent osmium-based pyridyl complexes, in particular,(bis(2,2′-bipyridine)[4′-methyl-4-(2-(4-(3-propyltrimethoxysilane)pyridinium)ethenyl)-2,2′-bipyridine]osmium(II)[tris(hexafluorophosphate)/tri-iodide],previously disclosed in WO 2006085319, andbis(2,2′-bipyridine)[4′-methyl-4-(2-(4-(3-propoxytrimethoxysilane)phenyl)ethenyl)-2,2′-bipyridine]osmium(II)[bis(hexafluorophosphate)/di-iodide], are able to selectively detect andquantify traces, i.e., ppm levels, of hexavalent chromium (Cr⁶⁺) in H₂Oand MeCN under acidic conditions. The measurements are relatively fast,i.e., about 1-min, and can be carried out under environmental conditionsand monitored in- and ex-situ using standard UV/visible spectroscopy(260-900 nm). The combined physicochemical properties and deviceperformance of such pyridyl complex-based monolayers, includingrobustness, regeneration, response time, stability and selectivity, aswell as the low detection limits, make this system an excellentalternative for detecting and quantifying Cr⁶⁺. Since osmium, iron andruthenium belong to the same group of chemical elements, i.e., havesimilar physicochemical properties, it is postulated that divalentiron/ruthenium-based pyridyl complexes will have a similar capacity.

Thus, in one aspect, the present invention relates to a hexavalentchromium (Cr⁶⁺) sensor device comprising a divalent osmium (Os²⁺)-, iron(Fe²⁺)- or ruthenium (Ru²⁺)-based pyridyl complex capable of changingits oxidation state in response to a reduction of Cr⁶⁺ at the presenceof H⁺, thereby causing a reversible and optically readable change inoptical properties of said complex. The device of the present inventionmay further comprise a substrate carrying a layered structure of saidpyridyl complex.

In another aspect, the present invention relates to an acidic aqueoussolution comprising a divalent osmium (Os²⁺)-, iron (Fe²⁺)- or ruthenium(Ru²⁺)-based pyridyl complex capable of changing its oxidation state inresponse to a reduction of Cr⁶⁺ at the presence of H⁺, for selectivedetection and quantification of Cr⁶⁺.

In further aspects, the present invention relates to an ampoulecontaining an acidic aqueous solution as defined above; as well as to akit containing at least two such ampoules.

In yet another aspect, the present invention provides a method forselective detection and quantification of Cr⁶⁺ in a liquid sample,comprising:

-   -   (i) exposing a divalent osmium (Os²⁺)-, iron (Fe²⁺)- or        ruthenium (Ru²⁺)-based pyridyl complex capable of changing its        oxidation state in response to a reduction of Cr⁶⁺ to said        sample, for a sufficient time period at the presence of H⁺;    -   (ii) recording absorption spectra of said pyridyl complex at the        UV/visible spectral range, preferably at the range of 400-900        nm; and    -   (iii) monitoring the presence of Cr⁶⁺ in said sample and        determining its concentration according to the change in the        absorption spectra of (ii) compared to a predetermined        absorption spectra of said pyridyl complex.

In still a further aspect, the present invention provides a method fordetoxification of Cr⁶⁺ in an aqueous or organic liquid media,comprising:

-   -   (i) contacting said liquid media with a divalent osmium (Os²⁺)-,        iron (Fe²⁺)- or ruthenium (Ru²⁺)-based pyridyl complex capable        of changing its oxidation state to Os³⁺-, Fe³⁺- or Ru³⁺-based        pyridyl complex, respectively, in response to a reduction of        Cr⁶⁺, for a sufficient time period at the presence of H⁺,        wherein said pyridyl complex is carried as a layered structure        on a substrate;    -   (ii) monitoring the presence of Cr⁶⁺ and determining its        concentration in a sample taken from said liquid media; and    -   (iii) when Cr⁶⁺ is detected in said sample, reducing said Os³⁺-,        Fe³⁺- or Ru³⁺-based pyridyl complex and repeating steps (i) and        (ii).

In yet a further aspect, the present invention provides a catalyticprocess for reduction of Cr⁺⁶, comprising reducing said Cr⁶⁺ with adivalent osmium (Os²⁺)-based pyridyl complex to thereby oxidize the Os²⁺to Os³⁺, and exposing the oxidized Os³⁺ to water for a sufficient timeperiod to thereby regenerate the Os³⁺ to Os²⁺.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows absorption spectra of (a) a solution (pH 1) of (0.85 mM)Cr⁶⁺ in MeCN; (b) a solution of 10.4 μM compound 10 in MeCN; and (c) amixed solution of 1 ml (20.8 μM) compound 10 and 1 ml (1.7 mM) Cr⁶⁺,both in MeCN at pH 1.

FIG. 2 shows absorption changes of the 10-based monolayer immersed in anacidified MeCN solution (pH=1) containing 0.5 ppm Cr⁶⁺. The inset showsthe absorption changes at λ=516 (▪) R²=0.990, λ=692 nm () R²=0.997,λ=317 nm (▴) R²=0.979, and λ=293 nm (▾) R²=0.850, at 4, 6, 10, 16, and45 min, respectively.

FIG. 3 shows the absorption changes in oxidation % after a 1-minexposure of the 10-based monolayer to aqueous solutions containing 0, 1,5 10, 25 or 50 ppm Cr⁶⁺ at pH=1. The black line represents a linear fit(R²=0.996). The dots show the results of a blind test, performed withstandard acidic (pH 1) aqueous solutions containing 3 and 28 ppm ofCr⁶⁺.

FIG. 4 shows absorption spectra of a typical switching experiment wherethe 10-based monolayer was oxidized for 1-min with an acidified MeCNsolution (pH<1) containing 5 ppm Cr⁶⁺, and subsequently reduced with H₂Owithin 3-min. the inset shows the spectral changes of the MLCT bands atλ=516 and 692 nm (long and short bars, respectively), as a function ofthe oxidation/reduction cycles.

FIG. 5 shows absorption of the 10-based monolayer at λ=516 nm afterimmersion for 1-min in an aqueous solution containing 100 ppm Cr⁶⁺ atdifferent pH values.

FIGS. 6A-6B show the optical response of the 10-based monolayer,expressed in reduction percentage, as a function of the pH. The pHdependent reduction of the 10-based monolayer with H₂O, whereinoxidation was performed with 50 ppm K₂Cr₂O₇ (R²=0.983) (6A); and the pHdependent reduction of the 10-based monolayer with H₂O, whereinoxidation was performed with 100 ppm NOBF₄ in MeCN(R²=0.996) (6B).

FIGS. 7A-7B show cyclic voltammogram for [Os(bpy)₃]Cl₂, in 0.1 M KClsolution in water at a scan rate of 100 mV/s between −1.6 and +1.0 V,with a glassy carbon working electrode and a Pt-wire counter electrodewith Ag/AgCl as reference, at pH 3.5 and pH 1 (7A); and cyclicvoltammogram for [Os(bpy)₃]Cl₂, in 0.1 M KCl solution in water at a scanrate of 400 mV/s, isolating the Os-metal center between 0 and 1 V, at pH3.5 and pH 1 (7B).

FIGS. 8A-8B show a plot of I_(p) vs. v^(1/2) for [Os(bpy)₃]Cl₂ at pH 1(8A) and pH 3.5 (8B), representing a linear correlation indicating adiffusion controlled oxidation/reduction process.

FIG. 9 shows relative oxidation change of the 10-based monolayer atλ=516 nm, after immersion in various aqueous matrices containing 5×10⁻⁴M of each of the following metals salts, with (row 1) and without (row2) the presence of 100 ppm Cr⁶⁺. a) HgCl₂, ZnCl₂, CuCl₂, CoCl₂, MnCl₂and NiCl₂; b) MgCl₂, BaCl₂ and CaCl₂; c) KCl, NaCl, CsCl and LiCl; d)LaCl₃, Al(NO₃)₃ and CdSO₄; e) NaNO₃, Na₂SO₄, Na₂SO₃, KH₂PO₄ and KBr; f)Pb(NO₃)₂ and NaNO₂; g) FeCl₃; and h) FeCl₃ after sample treatment with astrong base to selectively remove Fe³⁺.

FIG. 10 shows the absorption changes at λ=516 nm of the 10-basedmonolayer as a function of time upon immersion in aqueous solutions(pH 1) containing 80 ppm Cr⁶⁺ (▪) and Fe³⁺ (; R²=0.998). The linerepresented by the character ▪ represents the absorption of the 10-basedmonolayer after treatment with a strong base to selectively remove Fe³⁺,as described in Materials and Methods.

FIG. 11 shows optical response, expressed in oxidation %, of the10-based monolayer at λ=516 nm after immersion for 1-min in pond water(entries 1-5) and sand-extracted water (entries 6-9) under acidicconditions (pH=1). Entries 1 and 2 represent pond water with and withoutacid added to the sample, respectively; entries 3 and 4 represent 5 and10 ppm Cr⁶⁺, respectively, with the same amount of acid, except for a2-min response time; and entry 5 represents 100 ppm Cr⁶⁺. Entries 6 and7 represent water from the sand extraction, with and without acid addedto the sample; and entries 8 and 9 represent samples that were takenfrom the sand+Cr⁶⁺ extraction, in which the latter was acidified (pH=1).

FIG. 12 shows the stability of both MLCT bands at λ=516 and 692 uponimmersion the 10-based monolayer in acidic water (pH 1) for severalhours. The break indicates a 16 h break, during which the 10-basedmonolayer was not immersed in the acidic water.

FIG. 13 shows the oxidation change in %, as a function of time, of theMLCT band at λ=516 nm of the 10-based monolayer after exposure to thesolution, used in the experiment described in Example 9. The line showsan exponential fit with R²=0.993.

FIG. 14 shows electron spin resonance (ESR) spectrum of 2 mM solution ofCrCl₃ in H₂O at pH 1 (1); and a 1:1 (v:v) mixture of 2 mM K₂Cr₂O₇ and 6mM [Os(bpy)₃]Cl₂ in H₂O at pH 1 after 8 consecutive cycles, as describedin Example 9 (2).

FIG. 15 shows changes of the oxidation (▪) and reduction (♦) % of theMLCT at λ=516 nm of the 10-based monolayer as a function of the pH.Oxidation was done with 100 ppm Cr⁶⁺ (red dots), whereas as thereduction was done with H₂O.

FIG. 16 shows a graphical representation of a potential reactor forcatalytic detoxification of Cr⁶⁺ waste water with glass beadsfunctionalized with the 10-based monolayer. The magnification shows theprobable surface processes.

MODES FOR CARRYING OUT THE INVENTION

In one aspect, the present invention relates to a Cr⁶⁺ sensor devicecomprising a divalent osmium (Os²⁺)-, iron (Fe²⁺)- or ruthenium(Ru²⁺)-based pyridyl complex capable of changing its oxidation state inresponse to a reduction of Cr⁶⁺ at the presence of H⁺, thereby causing areversible and optically readable change in optical properties of saidcomplex. In a preferred embodiment, the sensor device of the presentinvention comprises Os²⁺-based pyridyl complex.

The term “oxidation state”, as used herein, refers to the electricallyneutral state or to the state produced by the gain or loss of electronsto an element, compound or chemical substituent/subunit. In a preferredembodiment, this term refers to states including the neutral state andany state other than a neutral state caused by the gain or loss ofelectrons (reduction or oxidation).

The term “optical properties”, as used herein, refers to the absorptionspectrum of the Os²⁺-, Fe²⁺- or Ru²⁺-based pyridyl complex used in theCr⁶⁺ sensor device of the present invention. The change in the opticalproperties is caused electrochemically by addition or withdrawal of oneor more electrons to or from the Os²⁺-, Fe²⁺- or Ru²⁺-based pyridylcomplex.

The term “pyridyl complex”, as used herein, refers to a metal having oneor more pyridyl ligands, i.e., the Os²⁺-, Fe²⁺- or Ru²⁺-based pyridylcomplex used in the Cr⁶⁺ sensor device of the present invention may beany pyridyl complex in which Os²⁺, Fe²⁺ or Ru²⁺ is coordinated to one ormore pyridyl ligands.

In one embodiment, the Os²⁺-, Fe²⁺- or Ru²⁺-based pyridyl complex ischarged tris-bipyridyl Os²⁺, Fe²⁺ or Ru²⁺-complex or a derivativethereof. More preferably, the Os²⁺-, Fe²⁺- or Ru²⁺-based pyridyl complexis a compound of the general formula I:

wherein M is Os, Fe or Ru; n is the formal oxidation state of the Os orFe, wherein n is 2 or 3; m is the positive charge of the tris-bipyridylligand, wherein m is an integer from 0 to 24, X is a counter anionselected from Br⁻, Cl⁻, F⁻, I⁻, PF₆ ⁻, BF₄ ⁻, OH⁻, ClO₄ ⁻, SO₃ ⁻,CF₃COO⁻, CN⁻, alkylCOO⁻, arylCOO⁻ or a combination thereof; and R₅ toR₂₈ is each independently selected from hydrogen, halogen, hydroxyl,azido, nitro, cyano, amino, substituted amino, thiol, C₁-C₁₀ alkyl,cycloalkyl, heterocycloalkyl, haloalkyl, aryl, heteroaryl, alkoxy,alkenyl, alkynyl, carboxamido, substituted carboxamido, carboxyl,protected carboxyl, protected amino, sulfonyl, substituted aryl,substituted cycloalkyl or substituted heterocycloalkyl, wherein at leastone of said R₅ to R₂₈ is a group A or B:

wherein

A is linked to the ring structure of the compound of general formula Ivia R₄; R₄ is selected from cis/trans C═C, C≡C, N═N, C═N, N═C, C—N, N—C,alkylene, arylene or a combination thereof; R₃ is C or N; R₂ is absentor is selected from hydrogen, alkyl, alkylene, aryl, arylene, OH,O-alkyl, O-alkylene or a combination thereof; and R₁ is absent or isselected from hydrogen, trialkoxysilane, trihalidesilane, thiol, COOH,COO⁻, Si(OH)₃ or phosphonate; and

B is —O(CH₂)_(p)—R₂₉ linked to the ring structure of the compound ofgeneral formula I via the oxygen, wherein p is an integer from 9 to 12;and R₂₉ is selected from hydrogen, trialkoxysilane, trihalidesilane,thiol, COOH, COO⁻, Si(OH)₃ or phosphonate; and

any two vicinal R₅-R₂₈ substituents, together with the carbon atoms towhich they are attached, may form a fused ring system selected fromcycloalkyl, heterocycloalkyl, heteroaryl or aryl, wherein said fusedsystem may be substituted by one or more groups selected from C₁-C₁₀alkyl, aryl, azido, cycloalkyl, halogen, heterocycloalkyl, alkoxy,hydroxyl, haloalkyl, heteroaryl, alkenyl, alkynyl, nitro, cyano, amino,substituted amino, carboxamido, substituted carboxamido, carboxyl,protected carboxyl, protected amino, thiol, sulfonyl or substitutedaryl; and said fused ring system may also contain at least oneheteroatom selected from N, O or S.

The term “alkyl”, as used herein, typically means a straight or branchedhydrocarbon radical having preferably 1-10 carbon atoms, and includes,e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl,tert-butyl, n-pentyl, isopentyl, 2,2-dimethylpropyl, n-hexyl, n-heptyl,n-octyl, n-nonyl, n-decyl and the like. The alkyl may further besubstituted. The term “alkylene” refers to a linear divalent hydrocarbonchain having preferably 1-10 carbon atoms and includes, e.g., methylene,ethylene, propylene, butylene, pentylene, hexylene, octylene and thelike.

The term “alkenyl” typically means a straight or branched hydrocarbonradical having preferably 2-10 carbon atoms and one or more doublebonds. Non-limiting examples of such alkenyls are ethenyl, 3-buten-1-yl,2-ethenylbutyl, 3-octen-1-yl, and the like. The term “alkenylene” refersto a linear divalent hydrocarbon chain having preferably 2-10 carbonatoms and one or more double bonds, and includes, e.g., 1-propylene,1-butylene, 2-butylene, 3-hexylene and the like.

The term “alkynyl” refers to a straight or branched hydrocarbon radicalhaving preferably 2-10 carbon atoms and containing at least one triplebond.

The term “cycloalkyl” typically means a saturated aliphatic hydrocarbonin a cyclic form (ring) having preferably 3-10 carbon atoms.Non-limiting examples of such cycloalkyl ring systems includecyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclodecyl and thelike. The cycloalkyl may be fused to other cycloalkyls, such in the caseof cis/trans decalin. The term “heterocycloalkyl” refers to acycloalkyl, in which at least one of the carbon atoms of the ring isreplaced by a heteroatom selected from N, O or S.

The term “alkylCOO” refers to an alkyl group substituted by a carboxylgroup (—COO—) on any one of its carbon atoms. Preferably, the alkyl has1-10 carbon atoms, more preferably CH₃COO⁻.

The term “aryl” typically means any aromatic group, preferably having6-14 carbon atoms such as phenyl and naphtyl. The aryl group may besubstituted by any known substituents. The term “arylCOO” refers to sucha substituted aryl, in this case being substituted by a carboxylategroup.

The term “heteroaryl” refers to an aromatic ring system in which atleast one of the carbon atoms is replaced by a heteroatom selected fromN, O or S. Non-limiting examples of heteroaryl include pyrrolyl, furyl,thienyl, pyrazolyl, imidazolyl, oxazolyl, isoxazolyl thiazolyl,isothiazolyl, pyridyl, 1,3-benzodioxinyl, pyrazinyl, pyrimidinyl,1,3,4-triazinyl, 1,2,3-triazinyl, 1,3,5-triazinyl, thiazinyl,quinolinyl, isoquinolinyl, benzofuryl, isobenzofuryl, indolyl,imidazo[1,2-a]pyridyl, pyrido[1,2-a]pyrimidinyl, benz-imidazolyl,benzthiazolyl and benzoxazolyl.

The term “halogen” includes fluoro, chloro, bromo, and iodo. The term“haloalkyl” refers to an alkyl substituted by at least one halogen.

The term “alkoxy” refers to the group —OR, wherein R is an alkyl group.The term “azido” refers to —N₃. The term “nitro” refers to —NO₂ and theterm “cyano” refers to —CN. The term “amino” refers to the group —NH₂ orto substituted amino including secondary, tertiary and quaternarysubstitutions wherein the substituents are alkyl or aryl. The term“protected amino” refers to such groups which may be converted to theamino group. The term “carboxamido” refers to the group —CONH₂ or tosuch a group substituted, in which each of the hydrogens is replaced byan alkyl or aryl group.

The term “carboxyl” refers to the group —COOH. The term “protectedcarboxyl” refers to such groups which may be converted into the carboxylgroup, e.g., esters such as —COOR, wherein R is an alkyl group or anequivalent thereof, and others which may be known to a person skilled inthe art of organic chemistry.

The term “trialkoxysilane” refers to a group of the general formula—Si(OR)₃, wherein each of the three R groups is an alkyl group, and maybe the same or different, preferably, trimethoxysilane ortriethoxysilane. Similarly, the term “trihalidesilane” refers to —SiX₃,wherein X is a halogen, each X may be same or different.

The expression “any two vicinal R₅-R₂₈ substituents” refers to any twosubstituents on the benzene rings, being ortho to one another. Theexpression “fused ring system” refers to at least two rings sharing onebond, such as in the case of naphthalene, phenanthrene, benzindole,benzpyridine and others. The fused ring system contains at least onebenzene ring, being the ring of the compound of general formula I andanother ring being formed by the ring closure of said any two vicinalR₄-R₂₇ substituents. The said another ring may be saturated orunsaturated, substituted or unsubstituted and may be heterocylic.

The compounds described in the specification, both the compounds offormula I, i.e., the Os²⁺-, Fe²⁺- or Ru²⁺-based pyridylcomplexes/compounds, as well as the starting compounds andintermediates, are herein identified by the Arabic numbers 1-15 in bold.However, since the pyridyl complexes specifically described herein aredefined with two different anions, each one of the compounds 4-15 hastwo forms designated “a” and “b”.

In one embodiment, the pyridyl complex is the compound of the generalformula I as defined above, wherein M is Os, Fe or Ru, n is 2, m is 0, Xis PF₆ ⁻ or I⁻, R₅, R₇ to R₂₆ and R₂₈ each is hydrogen, R₆ is methyl,and R₂₇ is A, wherein R₄ is C═C, R₃ is N, and R₂ and R₁ are both absent,i.e.,bis(2,2′-bipyridine)[4′-methyl-4-(2-(4-pyridyl)ethenyl)-2,2′-bipyridine]osmium(II)[bis(hexafluorophosphate)/di-iodide],herein designated compounds 4a-4-b, respectively;bis(2,2′-bipyridine)[4′-methyl-4-(2-(4-pyridyl)ethenyl)-2,2′-bipyridine]iron(II)[bis(hexafluorophosphate)/di-iodide],herein designated compounds 5a-5b, respectively; orbis(2,2′-bipyridine)[4′-methyl-4-(2-(4-pyridyl)ethenyl)-2,2′-bipyridine]ruthenium(II)[bis-(hexafluorophosphate)/di-iodide],herein designated compounds 6a-6b, respectively.

In another embodiment, the pyridyl complex is the compound of thegeneral formula I as defined above, wherein M is Os, Fe or Ru, n is 2, mis 1, X is PF₆ ⁻ or I⁻, R₅, R₇ to R₂₆ and R₂₈ each is hydrogen, R₆ ismethyl, and R₂₇ is A, wherein R₄ is C═C, R₃ is N, R₂ is methyl, and R₁is absent, i.e.,bis(2,2′-bipyridine)[4′-methyl-4-(2-(4-methylpyridinium)ethenyl)-2,2′-bipyridine]osmium(II)[tris(hexafluorophosphate)/tri-iodide],herein designated compounds 7a-7b, respectively;bis(2,2′-bipyridine)[4′-methyl-4-(2-(4-methylpyridinium)ethenyl)-2,2′-bipyridine]iron(II)[tris(hexafluorophosphate)/tri-iodide],herein designated compounds 8a-8b, respectively; orbis(2,2′-bipyridine)[4′-methyl-4-(2-(4-methylpyridinium)ethenyl)-2,2′-bipyridine]ruthenuim(II)[tris(hexafluorophosphate)/tri-iodide],herein designated compounds 9a-9b, respectively.

In a preferred embodiment, the pyridyl complex is the compound of thegeneral formula I as defined above, wherein M is Os, n is 2, m is 1, Xis PF₆ ⁻ or I⁻, R₅, R₇ to R₂₆ and R₂₈ each is hydrogen, R₆ is methyl,and R₂₇ is A, wherein R₄ is C═C, R₃ is N, R₂ is propyl, and R₁ istrimethoxysilane, i.e.,bis(2,2′-bipyridine)[4′-methyl-4-(2-(4-(3-propyltrimethoxysilane)pyridinium)ethenyl)-2,2′-bipyridine]osmium(II)[tris(hexafluorophosphate)/tri-iodide],herein designated compounds 10a and 10b, respectively.

In a further embodiment, the pyridyl complex is the compound of thegeneral formula I as defined above, wherein M is Os, Fe or Ru, n is 2, mis 0, X is PF₆ ⁻ or I⁻, R₅, R₇ to R₂₆ and R₂₈ each is hydrogen, R₆ ismethyl, and R₂₇ is A, wherein R₄ is C═C, R₃ is C, R₂ is OH, and R₁ isabsent, i.e.,bis(2,2′-bipyridine)[4′-methyl-4-(2-(4-hydroxyphenyl)ethenyl)-2,2′-bipyridine]osmium(II)[bis(hexafluorophosphate)/di-iodide],herein designated compounds 11a-11b, respectively;bis(2,2′-bipyridine)[4′-methyl-4-(2-(4-hydroxyphenyl)ethenyl)-2,2′-bipyridine]iron(II)[bis(hexafluorophosphate)/di-iodide],herein designated compounds 12a-12b, respectively; orbis(2,2′-bipyridine)[4′-methyl-4-(2-(4-hydroxyphenyl)ethenyl)-2,2′-bipyridine]ruthenium(II)[bis(hexafluorophosphate)/di-iodide],herein designated compounds 13a-13b, respectively.

In another preferred embodiment, the pyridyl complex is the compound ofthe general formula I as defined above, wherein M is Os, n is 2, m is 0,X is PF₆ ⁻ or I⁻, R₅, R₇ to R₂₆ and R₂₈ each is hydrogen, R₆ is methyl,and R₂₇ is A, wherein R₄ is C═C, R₃ is C, R₂ is O-propyl, and R₁ istrimethoxysilane, i.e.,bis(2,2′-bipyridine)[4′-methyl-4-(2-(4-(3-propoxytrimethoxysilane)phenyl)ethenyl)-2,2′-bipyridine]osmium(II)[bis(hexafluorophosphate)/di-iodide],herein designated compounds 14a and 14b, respectively.

In still further embodiments, the pyridyl complex is the compound of thegeneral formula I as defined above, wherein M is Os, n is 2, m is 0, Xis PF₆ ⁻ or I⁻, R₅, R₇ to R₂₆ and R₂₈ each is hydrogen, R₆ and R₂₇ eachis B, wherein p is 9 and R₂₉ is triethoxysilane, i.e.,bis(2,2′-bipyridine)[4,4′-dinonoxy-9-triethoxysilane-2,2′-bipyridine]osmium(II)[bis(hexafluorophosphate)/di-iodide],herein designated compounds 15a and 15b, respectively.

The various Os²⁺-, Fe²⁺- or Ru²⁺-based pyridyl complexes used accordingto the present invention can be prepared by any suitable method known inthe art, e.g., as disclosed in the aforesaid WO 2006085319 and US20070258147. In particular, the preparation of the Os²⁺-based pyridylcomplex 10 used in all the experiments conducted in accordance with thepresent invention, as well as the formation of 10-based monolayers onglass, are further described in Examples 1-2 hereinafter.

As shown in detail in the Examples section, trace amounts of Cr⁶⁺ inaqueous or organic solution could be detected in situ by monitoring theoptical properties of the 10-based monolayer by UV/visible spectroscopyin the transmission mode (260-900 nm). For example, immersing a 10-basedmonolayer on glass (0.8×2.5×0.1 cm) in an acidified MeCN solutioncontaining 0.5 ppm Cr⁶⁺ resulted in a significant decrease of theabsorption band at λ=293 nm and both singlet and triplet states ofmetal-to-ligand charge-transfer (MLCT) bands at λ=516 and 692 nm, and aconcurrent increase of the ligand-to-metal charge-transfer (LMCT) bandat λ=317 nm. Saturation of the sensor occurred under these reactionconditions after 45 min. The 10-based monolayer is stable in H₂O at pH=1for at least several hours in the absence of Cr⁶⁺, as judged byUV/visible spectroscopy.

Remarkably, the amount of Cr⁶⁺ could be accurately quantified withinonly 1-min of exposure time as well. The good linear correlation and thesystem stability allowed reliable and accurate quantification of Cr⁶⁺.For instance, a blind test showed that even after several weeks in air,the calibrated 10-based sensor can be used to determine the amount ofCr⁶⁺ within 10% accuracy. The detection range in H₂O and MeCN was 1-100ppm and 0.5-100 ppm, respectively. Reduction of the Os³⁺ system by watercompletely restored the MLCT bands at λ=516 and 692 nm to their originalvalues.

As further shown, the surface-solution redox chemistry is dependent onthe pH and shows good reversibility for at least 10 redox cycles. Exsitu UV/visible follow-up experiments demonstrated that the system onlyresponds to the analyte at a pH<3 for a 1-min exposure time, wherein thehighest oxidation rate is observed at pH=0.3. Interestingly, reductionof the sensor with H₂O was pH dependent as well. The maximum reductionrate was observed at pH=7.5, whereas at pH=1, hardly any reaction wasobserved. The monolayer setup became unstable at higher pH values, whichis common for siloxane-based monolayers.

The selectivity of the 10-based monolayer towards Cr⁶⁺ was demonstratedusing a series of aqueous matrices containing various metal ions, oranions commonly found in groundwater. Only samples containing Cr⁶⁺induced significant optical changes (ΔA≧60%) after a 1-min exposuretime.

Whereas in the absence of H⁺, the 10-based sensor does not respond toCr⁶⁺, we recently reported that under such conditions, the 10-basedmonolayer is capable of optically sensing Fe³⁺ in H₂O and MeCN.Apparently, this dual sensor system is capable of detecting a specificmetal ion by varying the pH. Time-dependent measurement of the oxidationof the 10-based monolayer by aqueous solutions containing 80 ppm Fe³⁺ orCr⁶⁺ showed that the optical response of the sensor towards the latterion is at least 6 times greater within 1-min of exposure time. Moreover,Fe³⁺ can selectively be removed from the medium by treatment with strongbase prior to analysis of the Cr⁶⁺ content by the 10-based monolayer.Cr⁶⁺ is stable under basic conditions.

The formation of device quality sensors requires not only the ability todetect analytes under controlled laboratory conditions, but also underenvironmental conditions. As shown, the 10-based monolayer has also beenused to detect Cr⁶⁺ in environmental samples. Water from a fishing pondand playground sand samples were collected and analyzed with and withoutthe addition of ppm-levels of Cr⁶⁺. The Cr⁶⁺ was extracted from the sandwith water. All water samples were acidified to pH=1. Only contaminatedsamples gave positive responses.

In view of the aforesaid, in one embodiment, the optical properties ofthe Os²⁺-, Fe²⁺- or Ru²⁺-based pyridyl complex are optical absorptionspectra of said pyridyl complex at the UV/visible spectral range,preferably at the range of 400-900 nm.

In another embodiment, the Cr⁶⁺ sensor device of the present inventioncomprises a divalent Os²⁺-based pyridyl complex, wherein said device isfurther capable of changing its oxidation state in response to areduction of Fe³⁺ at neutral pH, for detection of Fe³⁺.

The Cr⁶⁺ sensor device of the present invention may further comprise asubstrate carrying a layered structure of the Os²⁺-, Fe²⁺- or Ru²⁺-basedpyridyl complex as defined above.

In one embodiment, the layered structure of the Os²⁺-, Fe²⁺- orRu²⁺-based pyridyl complex comprises a monolayer of said pyridylcomplex.

In another embodiment, the layered structure of the Os²⁺-, Fe²⁺- or Ru²⁺-based pyridyl complex comprises a plurality of identical or differentlayers of said pyridyl complex.

In a further embodiment, (i) the pyridyl complex is bound to a linkerdesigned to covalently bind to the surface of said substrate; or (ii)the surface of said substrate carries a functional group capable ofcoordinating or binding to said layered structure. In a preferredembodiment, the functional group is capable of either covalently ornon-covalently binding to said layered structure. The linker may be,without being limited to, a saturated or unsaturated, substituted orunsubstituted alkylene; a saturated or unsaturated, substituted orunsubstituted alkylaryl group; or a saturated or unsaturated,substituted or unsubstituted heterocycloalkyl groups, wherein saidlinker is attached to a functional group. Non-limiting examples offunctional groups, when attached either to the linker or to the surfaceof the substrate, include silanes, thiols, phosphonates and alkenes.

In yet a further embodiment, the substrate is hydrophilic, hydrophobicor a combination thereof.

In one embodiment, the substrate includes a material selected fromglass, a doped glass, indium tin oxide (ITO)-coated glass, silicon, adoped silicon, Si(100), Si(111), SiO₂, SiH, silicon carbide mirror,quartz, a metal, metal oxide, a mixture of metal and metal oxide, groupIV elements, mica, a polymer such as polyacrylamide and polystyrene, aplastic, a zeolite, a clay, wood, a membrane, an optical fiber, aceramic, a metalized ceramic, an alumina, an electrically-conductivematerial, a semiconductor, steel or a stainless steel. In preferredembodiments, the substrate as defined hereinabove is in the form ofbeads, microparticles, nanoparticles, quantum dots or nanotubes.

In one embodiment, the substrate is optically transparent to the UV andvisible spectral ranges.

In a most preferred embodiment, the Cr⁶⁺ sensor device of the presentinvention comprises a substrate carrying a layered structure of anOs²⁺-based pyridyl complex as defined above, wherein said substrate isglass, more preferably glass slides or beads, said pyridyl complex isthe compound of the general formula I wherein M is Os, n is 2, m is 1, Xis PF₆ ⁻ or I⁻, R₅, R₇ to R₂₆ and R₂₈ each is hydrogen, R₆ is methyl,and R₂₇ is A, wherein R₄ is C═C, R₃ is N, R₂ is propyl, and R₁ istrimethoxysilane (compounds 10a or 10b, respectively), and a monolayerof said pyridyl complex is covalently bound to said substrate.

In another aspect, the present invention relates to an acidic aqueoussolution comprising a divalent osmium (Os²⁺)-, iron (Fe²⁺)- or ruthenium(Ru²⁺)-based pyridyl complex capable of changing its oxidation state inresponse to a reduction of Cr⁶⁺ at the presence of H⁺, for selectivedetection and quantification of Cr⁶⁺.

The pyridyl complex comprised within the acidic aqueous solution of thepresent invention may be any Os²⁺-, Fe²⁺- or Ru²⁺-based pyridyl complexas defined above such as, without being limited to, any one of compounds4-15.

In one embodiment, the solution of the present invention comprisesOs²⁺-based pyridyl complex as defined above. In a preferred embodiment,the solution has a pH at the range of 0.1-3, preferably 0.3-2, mostpreferably about 1.

In a further aspect, the present invention relates to an ampoulecontaining an acidic aqueous solution as defined above.

In yet a further aspect, the present invention relates to a kitcontaining at least two ampoules as defined above.

In still another aspect, the present invention provides a method forselective detection and quantification of Cr⁶⁺ in a liquid sample,comprising:

-   -   (i) exposing a divalent osmium (Os²⁺)-, iron (Fe²⁺)- or        ruthenium (Ru²⁺)-based pyridyl complex capable of changing its        oxidation state in response to a reduction of Cr⁶⁺ to said        sample, for a sufficient time period at the presence of H⁺;    -   (ii) recording absorption spectra of said pyridyl complex at the        UV/visible spectral range, preferably at the range of 400-900        nm; and    -   (iii) monitoring the presence of Cr⁶⁺ in said sample and        determining its concentration according to the change in the        absorption spectra of (ii) compared to a predetermined        absorption spectra of said pyridyl complex.

The pyridyl complex used according to this method may be any Os²⁺-,Fe²⁺- or Ru²⁺-based pyridyl complex as defined above such as, withoutbeing limited to, any one of compounds 4-15.

In another embodiment, the pyridyl complex used according to this methodis carried as a layered structure on a substrate as defined above.

In one embodiment, the liquid sample analyzed according to this methodis obtained as a result of treating a solid sample by a liquid media.

In one embodiment, the pyridyl complex used according to this method isOs²⁺-based pyridyl complex as defined above. In a preferred embodiment,a decrease of the metal to ligand charge transfer (MLCT) bands at λ=516and 692 nm indicates the presence of Cr⁶⁺, and the percentage of saiddecrease is proportional to the concentration of Cr⁶⁺ in said sample. Inanother preferred embodiment, the Os²⁺-based pyridyl complex is exposedto the sample analyzed at a pH in a range of 0.1-3, preferably 0.3-2,most preferably about 1, and the Os²⁺-based pyridyl complex is exposedto the sample analyzed for about 1 min.

As shown in the Examples section hereinafter, the Cr⁶⁺ detection methodis redox coupled, i.e., associated with the oxidation of the 10-basedmonolayer from Os²⁺ to Os³⁺, followed by Cr³⁺ generation; and theoxidation of the Os metal center may be reversibly switched in solution,depending of the pH, with subsequent Cr³⁺ formation. In view of that, achemically surface bound 10-based monolayer may effectively be appliedin a reactor for Cr⁶⁺ waste water treatment, i.e., for Cr⁶⁺detoxification. As particularly shown in Example 9, the Cr⁶⁺detoxification process is, in fact, a catalytic process, in which Cr⁶⁺is reduced with Os²⁺-based pyridyl complex to thereby oxidize the Os²⁺to Os³⁺, and the Os³⁺ is then exposed to water, to thereby regeneratethe Os³⁺ to Os²⁺.

Thus, in yet another aspect, the present invention provides a method fordetoxification of Cr⁶⁺ in an aqueous or organic liquid media,comprising:

-   -   (i) contacting said liquid media with a divalent osmium (Os²⁺)-,        iron (Fe²⁺)- or ruthenium (Ru²⁺)-based pyridyl complex capable        of changing its oxidation state to Os³⁺-, Fe³⁺- or Ru³⁺-based        pyridyl complex, respectively, in response to a reduction of        Cr⁶⁺, for a sufficient time period at the presence of H⁺,        wherein said pyridyl complex is carried as a layered structure        on a substrate;    -   (ii) monitoring the presence of Cr⁶⁺ and determining its        concentration in a sample taken from said liquid media; and    -   (iii) when Cr⁶⁺ is detected in said sample, reducing said Os³⁺-,        Fe³⁺- or Ru³⁺-based pyridyl complex and repeating steps (i) and        (ii).

The pyridyl complex used according to this method may be any Os²⁺-,Fe²⁺- or Ru²⁺-based pyridyl complex as defined above such as, withoutbeing limited to, any one of compounds 4-15.

In one embodiment, the substrate is in the form of beads, nanoparticles,quantum dots or nanotubes.

The monitoring of the presence of Cr⁶⁺ and the determination of itsconcentration in step (ii) of this method may be carried out by anysuitable method known in the art, e.g., by flame atomic absorptionspectrometry (FAAS), inductively coupled plasma atomic emissionspectrometry (ICP-AES), chemiluminescence, X-ray fluorescence,electrochemical methods or by the method for selective detection andquantification of Cr⁶⁺ in a liquid sample as defined above.

In one embodiment, the pyridyl complex used according to this method isOs²⁺-based pyridyl complex as defined above. In a preferred embodiment,the Os²⁺-based pyridyl complex is contacted with the sample treated at apH in a range of 0.1-3, preferably 0.3-2, most preferably about 1.

In yet a further aspect, the present invention provides a method fordetoxification of Cr⁶⁺ in an aqueous or organic liquid media, comprisingcontacting said liquid media with a divalent osmium (Os²⁺)-, iron(Fe²⁺)- or ruthenium (Ru²⁺)-based pyridyl complex capable of changingits oxidation state to Os³⁺, Fe³⁺ or Ru³⁺-based pyridyl complex,respectively, in response to a reduction of Cr⁶⁺, for a sufficient timeperiod at the presence of H⁺, wherein said pyridyl complex is carried asa layered structure on a substrate.

In still a further aspect, the present invention provides a catalyticprocess for reduction of Cr⁺⁶, comprising reducing said Cr⁶⁺ with adivalent osmium (Os²⁺)-based pyridyl complex to thereby oxidize the Os²⁺to Os³⁺, and exposing the oxidized Os³⁺ to water for a sufficient timeperiod to thereby regenerate the Os³⁺ to Os²⁺.

The invention will now be illustrated by the following non-limitingExamples.

EXAMPLES Materials and Methods

General. Most metal salts were purchased from BDH or Merck. MgCl₂ waspurchased from Aldrich. All chemicals where used as received. Solvents(Reagent Grade) were purchased from Bio-Lab (Jerusalem), Frutarom(Haifa) or Mallinckrodt Baker (Phillipsburg, N.J.). [Os(bpy)₃]Cl₂ wasprepared by a modification of the procedure described by Johnson et al.(1988) with NH₄OsCl₆, ethylene glycol, while purification was done byprecipitation with Et₂O. The monolayers were synthesized andcharacterized as previously reported (Gupta et al., 2006). Soda-Limeglass used for monolayer preparation was cleaned by washing severaltimes with deionised (DI) water, followed by immersion in a piranhasolution (7:3 (v:v) H₂SO₄:30% H₂O₂) for 1 h (Caution: piranha is anextremely dangerous oxidizing agent thus should be carefully handledusing appropriate personal protection). The glass substrates were againcleaned after the piranha treatment with DI water and placed in RCA(1:5:1 (v:v:v) NH₄OH:H₂O:30% H₂O₂) for 1 h. Subsequently, the substrateswere rinsed with isopropanol, dried under N₂ flow and oven dried for 2h. UV/visible spectra were recorded at room temperature, unless statedotherwise, on a Cary 100 spectrophotometer in transmission mode (260-900nm). The functionalised glass substrates were fixed in a Teflon holder(1.5×0.75 cm window) and an identical glass substrate without monolayerwas used to compensate for the background absorption.

Optical detection of Cr⁶⁺ in solution. A stock solution of 1000 ppmK₂Cr₂O₇ in MeCN was prepared by dissolving 16 mg K₂Cr₂O₇ in 1 ml waterwhereafter 19 ml MeCN was added. This solution was diluted twice andacidified with 60 μl 32% HCl, and the UV/visible spectrum was recordedusing MeCN as a background. The same was done with a MeCN solution ofcompound 10. After both spectra were taken, the two solutions were mixedtogether and the UV/visible spectrum was immediately recorded with aK₂Cr₂O₇ solution as the background reference.

Time-dependent oxidation of the 10-based monolayer by Cr⁶⁺. A stocksolution of 1000 ppm K₂Cr₂O₇ in MeCN was prepared as described above.The 10-based monolayer was immersed in an acidified MeCN (pH 1) 0.5 ppmK₂Cr₂O₇ solution for 2, 4, 6-16 min. The glass substrate was dried atroom temperature and gently wiped with task paper and the UV/visiblespectrum was then recorded.

pH dependence of Cr⁶⁺ detection. 100 ppm K₂Cr₂O₇ solutions in DI waterat a pH ranging from 7 to 0 were prepared by adding a specified amountof 1M HCl to the K₂Cr₂O₇ solutions, with increments of 0.5 pH unitsbetween pH 0-3, and with increments of 1 pH unit between pH 3-7. The10-based monolayer was immersed in the various solutions for 1 min,subsequently dried and gently wiped with task paper, and the UV/visiblespectra were then recorded. After each experiment, the 10-basedmonolayer was reset as described above. Removal of the monolayer fromthe glass substrates was observed by UV/visible spectroscopy at pH>9.

Selective sensing of Cr⁶⁺ in aqueous matrices. A stock solution of 1000ppm of K₂Cr₂O₇ in DI water was prepared by dissolving 20 mg K₂Cr₂O₇ in20 ml water. Stock solutions of each one of the metal salts used wereprepared by dissolving 5×10⁻⁴ mol of the corresponding metal salt in 100ml DI water. A typical experiment was carried out as follows: Theaqueous metal salt solution (1 ml) was further diluted with 8 ml DIwater, and 100 μl of 32% HCl was then added. The 10-based monolayer wasimmersed in the obtained solution for 1 min and after drying, theUV/visible spectrum was recorded. Then, 1 ml of the K₂Cr₂O₇ stocksolution was added to the same aqueous metal salt solution, themonolayer was again immersed for 1 min, and the UV/visible spectrum wasrecorded.

Effect of Fe³⁺ on the oxidation of the sensor by Cr⁶⁺. Aqueous solutionsat pH 1 were prepared, containing 80 ppm of FeCl₃ or K₂Cr₂O₇. The10-based monolayer was immersed for 5 min in a FeCl₃ solution and theUV/visible spectrum was recorded with 1 min time intervals. The same wasdone with the Cr⁶⁺ solution, only for a 3 min time window, sincesaturation of the sensor was already achieved after 1 min exposure time.The same FeCl₃ sample was made basic, pH 14, while after Fe³⁺precipitated as its hydroxide. The solution was filtered using 2 μm poreTeflon filter, and the filtrate was reacidified to pH 1. The 10-basedmonolayer was then immersed again for 5 min, during which the UV/visiblespectrum was recorded with 1 min time intervals.

Environmental detection of Cr⁶⁺. (a) A water sample was collected from apond located at the campus of the Weizmann Institute of Science(Rehovot, Israel) and divided into two fractions of 10 and 9 mlrespectively. One ml of 1000 ppm K₂Cr₂O₇ was added to the latter sample,and both samples were acidified with 100 μl 32% HCl. The 10-basedmonolayer was immersed in both samples for 1 min, and their UV/visiblespectra were then recorded. The same was done with K₂Cr₂O₇concentrations of 5 and 10 ppm respectively, with 2 min immersion time.(b) A 100 g sand sample was collected from a playground located at thecampus of the Weizmann Institute of Science and divided into twoportions of 20 g each, and 10 mg K₂Cr₂O₇ was then added to one of theportions. 100 ml DI water were added to both portions and thenvigorously stirred for 2 h under heating (60° C.). Both solutions werethen filtered, and 10 ml of the filtrates were collected. After coolingto room temperature, 100 μl 32% HCl was added to each one of thecollected filtrates, and the 10-based monolayer was immersed for 1 minin both solutions. Then, the substrate was dried and gently wiped withtask paper and the UV/visible spectrum was recorded.

pH dependence of the H₂O oxidation. Water samples with different pHvalues ranging between 1-7.5, with increments of 1 pH unit, as well as a50 ppm aqueous solution of K₂Cr₂O₇ at pH 1 were prepared. The 10-basedmonolayer was fully oxidized by immersion for 3 min in the 50 ppmaqueous K₂Cr₂O₇ solution and subsequently washed for 1 min in dry MeCN,and the UV/visible spectrum was then recorded to confirm full oxidationof the 10-based monolayer. When fully oxidized, the monolayer wasimmersed for 3 min in water at pH 1. The glass substrate was then driedand gently wiped with task paper and the UV/visible spectrum wasrecorded. This procedure was repeated for all the water samples atdifferent pH values, and was further used when the 10-based monolayerwas oxidized with a 100 ppm NOBF₄ solution in dry MeCN.

Detection of Cr³⁺ by electron spin resonance (ESR). A 10 ml 6 mM aqueoussolution of [Os(bpy)₃]Cl₂ at pH 1, and a 10 ml 2 mM aqueous solution ofK₂Cr₂O₇ at pH 1 were prepared. Subsequently, 2 ml of both solutions weremixed together, and a gradual color change was observed from dark greento red/purple. Directly after mixing, the ESR spectrum of the mixedsolution was recorded.

Example 1 Preparation of the Os²⁺-Based Pyridyl Complex 10

In order to prepare the Os²⁺-based pyridyl complex 10, compound 3 wasfirst synthesized starting from compound 1, using a modified literatureprocedure (Kim and Shin, 2003), and the preparation of compound 10 fromcompound 3 was performed in two steps as previously described (Gupta etal., 2006). As particularly depicted in Scheme 1 hereinafter, thepreparation of compound 10 included the following steps:

(i) Synthesis of 4′-methyl-4-(2-(4-pyridyl)ethan-2-ol)-2,2′-bipyridine,2. A solution of 4,4′-dimethyl-2,2′-bipyridine, 1 (2.2 g, 11.9 mmol), intetrahydrofuran (THF, 50 ml) was prepared under Argon, and freshlyprepared lithiumdiisopropylamine (LDA) (8 ml, 12.6 mmol, BuLi and 1.6ml, 12.7 mmol diisopropylamine in 16 ml THF) was added to the solutionwhile stirring during 30 min at 0° C. After 1 h of additional stirring,4-pyridinecarboxy aldehyde (1.2 ml, 12.8 mmol) in 10 ml THF was addeddropwise, and the solution was allowed to stir overnight whereupon thecolor changed from green to orange. The reaction was quenched with waterand the THF was evaporated under reduced pressure. The remainingsolution was extracted (3×100 ml) with CH₂Cl₂, and the organic layer wasthen washed with saturated NaCl and dried with Na₂SO₄. Thereafter, thesolvent was removed under reduced pressure and the residue was purifiedusing column chromatography (150 g neutral alumina G-II). The eluent waschanged from CH₂Cl₂ to 2% MeOH in CH₂Cl₂ as the starting material wasidentified on thin layer chromatography (TLC), yielding 1.3 g, 25%,compound 2 as a light yellow/orange solid, as identify by TLC (2% MeOHin CH₂Cl₂).

(ii) Synthesis of 4′-methyl-4-(2-(4-pyridyl)ethynyl)-2,2′-bipyridine, 3.Compound 2 (2.9 g, 9.9 mmol) was dried for 0.5 h under vacuum, and drypyridine (24 ml) was then added under Argon. Using schlenk techniques, asolution of POCl₃ (3.9 ml, 41.8 mmol) in dry pyridine (16 ml) wasprepared and added dropwise during 30 min at room temperature, to thesolution of compound 2, and the solution was allowed to stir for atleast additional 1 h. The pyridine was carefully removed under vacuumand the residue was dissolved in water. The pH of the aqueous solutionwas adjusted to pH 7-8 with a concentrated NaOH solution, and thesolution was extracted (3×100 ml CH₂Cl₂). The organic layers werecombined, washed with saturated NaCl and dried with Na₂SO₄. The solventwas removed under reduced pressure and the residue was purified usingcolumn chromatography (150 g neutral alumina G-II) while graduallyincreasing the solvent polarity from CH₂Cl₂ to 2% MeOH in CH₂Cl₂,yielding 0.65 g (50%) of compound 3 as a light yellow solid. Thestructure and purity of compound 3 was verified by TLC (2% MeOH inCH₂Cl₂) and ¹H NMR spectroscopy.

(iii) Preparation ofbis(2,2′-bipyridine)[4′-methyl-4-(2-(4-pyridyl)ethenyl)-2,2′-bipyridine]osmium(II)[bis(hexaflaorophosphate)/di-iodide],4. Os(bpy)₂Cl₂].2H₂O (200 mg, 0.328 mmol) was reacted with compound 3(107 mg, 0.39 mmol) under reflux in 50 ml ethanol-water (1:1, v:v) for24 h to provide a dark green solution, which was concentrated to ˜10 mlunder vacuum. Compound 4 was precipitated by addition of an excess of asaturated NH₄PF₆ solution in water (150 mg in 3 ml). The precipitate waswashed with an excess of water (100 ml) and afterwards with diethylether(50 ml), and was then purified by column chromatography (neutralalumina, G-III) using toluene/MeCN (8:2 v:v) as eluent. The second greenfraction was collected and dried under vacuum to afford compound 4(yield: 220 mg, 63%). The structure and purity of compound 4 wasverified by ¹H and ¹³C NMR spectroscopy and mass spectroscopy.

(iv) Preparation of bis(2,2′-bipyridine)[4′-methyl-4-(2-(4-(3-propyltrim ethoxysilane)pyridinium)ethenyl)-2,2′-bipyridine]osmium(H)[tris(hexafluorophosphate)/tri-iodide], 10. 3-iodopropyltrimethoxy silane (67mg, 0.23 mmol) in excess was added to a dry THF/MeCN (9:1 v:v) solution(20 ml) of compound 4 (50 mg, 0.047 mmol) under N₂ in a pressure vessel.The reaction mixture was stirred at 90° C. for 72 h and the volume wasthen reduced to ˜2 ml. The addition of dry pentane (15 ml) resulted inthe precipitation of compound 10 at room temperature. The solvent wasdecanted and washed with dry pentane (3×60 ml) under vacuum to affordcompound 10 (yield: 56 mg, 88%). The structure and purity of compound 10was verified by ¹H and ¹³C NMR spectroscopy and mass spectroscopy.

Importantly, when the concentrations of compound 2 andphosphoroxychloride where increased, considerable better yields, i.e.,50-75%, were obtained.

Example 2 Formation of Compound 10-Based Monolayers on Glass

Monolayers of compound 10 on glass were formed as previously describedand are illustrated in Scheme 2 hereinafter. In particular, freshlycleaned glass substrates (0.1×0.8×2.5 cm) were loaded under N₂atmosphere into a pressure tube that contained a 0.5 mM solution ofcompound 10 in acetonitrile/toluene (3:7 v:v). The pressure tube wassealed and allowed to react for 52 h at 85° C., and the functionalizedsubstrates were then rinsed with acetonitrile under N₂ atmosphere andsonicated for 8 mM each in acetonitrile, acetone and isopropanol. Thesamples were dried under N₂ flow and stored in the dark.

These monolayers are robust and have previously been characterized withatomic force microscopy (AFM) and UV/visible spectroscopy (Gupta et al.,2006). As has further been shown (Gupta et al., 2006, 2007; Gupta andvan der Boom, 2006, 2007; Gulino et al., 2007), the UV/visible spectrumof the 10-based monolayer shows characteristic metal-to-ligandcharge-transfer (MLCT) bands at λ=692 and 516 nm respectively, which canbe addressed by changing the metal oxidation state of the d⁶ metalcentre. For instance, oxidation of Os²⁺ to Os³⁺ induces the bleaching ofthe MLCT bands with a subsequent increase of the ligand-to-metalcharge-transfer (LMCT) band at λ=317 nm. This has previously beenexploited to detect H₂O, NO⁺ in organic solvents, Fe³⁺ in organic andaqueous media, and NO_(x) in the gasphase.

Example 3 Cr⁶⁺ Oxidizes Compound 10

Since Cr⁶⁺ undergoes reduction in solution in the presence of H⁺ andlow-valent metal centers such as Fe²⁺, Mn²⁺ and V³⁺, it was speculatedthat such a reaction would also be possible between Os²⁺ and Cr⁶⁺. Forthis reaction, acidic conditions are required as it is well known thatK₂Cr₂O₇ is a strong oxidizing agent only under acidic conditions(E^(o)=+1.33 V), whereas under basic conditions it is a poor oxidizer(E^(o)=−0.13 V). Indeed, reaction of compound 10 (20.8 μM) in MeCN withan excess (1.7 mM) of K₂Cr₂O₇ in MeCN, at pH 1, resulted in electrontransfer from the osmium metal center to the Cr⁶⁺ metal center, asindicated by the characteristic bleaching of the MLCT bands at λ=516 and692 nm and the increase of the LMCT band at λ=312 nm, and shown inFIG. 1. The electron transfer was also confirmed by electron spinresonance (ESR) that showed the formation of Cr³⁺ by reacting a 6 mMaqueous solution of [Os(bpy)₃)Cl₂ with 2 mM aqueous solution of K₂Cr₂O₇at pH 1.

Example 4 Compound 10 Optically Recognizes ppm Levels of Cr⁶⁺

As found in a series of experiments, using K₂Cr₂O₇ as the Cr⁶⁺ source,trace amounts of Cr⁶⁺ in aqueous or organic solution can be detected insitu by monitoring the optical properties of the 10-based monolayer byUV/visible spectroscopy in the transmission mode (260-800 nm). Inparticular, immersing a 10-based monolayer on glass (0.8×2.5×0.1 cm) inan acidified MeCN solution containing 0.5 ppm Cr⁶⁺ resulted in asignificant decrease of the absorption band at λ=293 nm and both singletand triplet states of metal-to-ligand charge-transfer (MLCT) bands atλ=516 and 692 nm, and a concurrent increase of the ligand-to-metalcharge-transfer (LMCT) band at λ=317 nm, as shown in FIG. 2. As furthershown in FIG. 2 (inset), saturation of the sensor occurred under thesereaction conditions after 45 minutes. The 10-based monolayer was stablein H₂O at pH=1 for at least several hours in the absence of Cr⁶⁺, asindicated by UV/visible spectroscopy.

In order to evaluate its Cr⁶⁺ sensing quality, the 10-based monolayerwas immersed for 1 min in aqueous (pH 1) solutions containing variousconcentrations (0, 1, 5, 10, 25 or 50 ppm) of K₂Cr₂O₇, where aftersubsequently their UV/visible absorption spectra were recorded, and arepresentative calibration curve of the 10-based monolayer with thesesolutions is shown in FIG. 3. The good linear correlation and the systemstability allowed reliable and accurate quantification of Cr⁶⁺, and wasfurther verified by performing a blind test with standard acidic (pH 1)aqueous solutions containing 3 and 28 ppm of Cr⁶⁺. As particularly shownin FIG. 3, the blind test showed that even after several weeks in air,the calibrated 10-based sensor could be used to determine the amount ofCr⁶⁺ within 10% accuracy. The detection range in H₂O and MeCN was 1-100ppm and 0.5-100 ppm, respectively. Reduction of the Os³⁺ system by watercompletely restores the MLCT bands at λ=516 and 692 nm to their originalvalues, as shown in FIG. 4 (Gupta and van der Boom, 2006, 2007; Gupta etal., 2006; For water-mediated reduction of Ru³⁺ and Os³⁺ complexes insolution, see: Zong and Thummel, 2005; Hurst, 2005; Lay and Sasse,1985).

Example 5 Catalytic Properties of the 10-Based Monolayer

In this experiment, the effect of consecutive oxidation/reduction cycleson the 10-based monolayer, i.e., its oxidation/reduction reversibility,was examined. In particular, the 10-based monolayer sensor was immersedin a 5 ppm K₂Cr₂O₇ solution in acidic MeCN (pH 1) for 1 min, whereafter;it was reset by immersing for 1 min in MeCN, quick washing with basicwater (pH˜8) and then immersing again in water for 3 min. After eachoxidation/reduction cycle, the substrates were subsequently dried andgently wiped with task paper and the UV/visible spectrum was recorded.These cycles were repeated up to 10 times to show completereversibility. As shown in FIG. 4, the surface-solution redox chemistryis dependent on the pH and shows good reversibility for at least 10redox cycles. The complete reversibility of the of the 10-basedmonolayer is particularly shown in the inset of this figure, whereinnegative values correspond to the “oxidative” bleaching of the MLCTbands and positive values correspond to the “reductive” restoration ofthese bands, indicating that every oxidation/reduction cycle causedabout the same change, ΔA, for the oxidation and the reduction process.

Ex situ UV/visible follow-up experiments, as described in Materials andMethods, demonstrated that the system responds to the analyte only at apH<3 for a 1-min exposure time, as shown in FIG. 5. The highestoxidation rate was observed at pH=0.3. Interestingly, reduction of thesensor with H₂O was pH dependent as well. The maximum reduction rate wasobserved at pH=7.5, whereas at pH=1, hardly any reaction is observed.The monolayer setup became unstable at higher pH values, which is commonfor siloxane-based monolayers (Wasserman et al., 1989).

The pH dependence of the water oxidation of the 10-based monolayer wasevaluated as described in Materials and Methods, and the opticalresponse of the 10-based monolayer, expressed in reduction % as afunction of pH, is shown in FIGS. 6A-6B. As particularly found, therecovery of the 10-based monolayer at low pH values was ratherdifficult, in contrast to neutral pH values where 100% recovery wasobserved, suggesting that the pH might have an interesting effect on theelectrode potential of the used 10-based monolayer. Therefore,[Os(bpy)₃]Cl₂, closely resembles the confined osmium-complex on glass,was chosen, and its cyclic voltammograms in 0.1 M KCl solution) areshown in FIGS. 7A-7B.

In water, the first oxidation process at E=0.61 V is associated with theoxidation of Os²⁺ to Os³⁺. This process is reversible and indicated by apeak separation of 60 mV and a linear correlation between I_(p) andv^(1/2), characteristic for reversible processes (FIGS. 8A-8B). As shownin FIG. 7B, there was no significant effect of the pH on the redoxpotential of the Os-metal center, i.e., the oxidation/reductionpotentials were only shifted 20 mV upon acidification from pH 3.5 to 1,while increasing the pH from 3.5 to 12 did not lead to any change in thecyclic voltammogram. In water, however, only one irreversible oxidationpeak was observed for the bipyridine ligand around −1.3 V, instead oftwo oxidation processes observed in MeCN (Matsumurainoue et al., 1986).In view of that it is suggested that the pH has no effect on the redoxpotential of [Os(bpy)₃]Cl₂, thus the pH dependence must be caused by amechanistic effect.

Example 6 Compound 10 is Highly Selective to Cr⁶⁺ in the Presence of H⁺

In order to test the selectivity of the 10-based monolayer towards Cr⁶⁺,a series of aqueous solutions containing various metal ions, e.g.,alkali, alkaline earth and transition metal ions, or anions commonlyfound in groundwater (Förstner and Wittman, 1981) were prepared asdescribed in Materials and Methods, and the relative oxidation change ofthe 10-based monolayer at λ=516 nm, after immersion in each one of thesesolutions, with and without the presence of Cr⁶⁺, was tested. Thespecific solutions prepared and used in this experiment consisted of (a)HgCl₂, ZnCl₂, CuCl₂, CoCl₂, MnCl₂ and NiCl₂; (b) MgCl₂, BaCl₂ and CaCl₂;(c) KCl, NaCl, CsCl and LiCl; (d) LaCl₃, Al(NO₃)₃ and CdSO₄; (e) NaNO₃,Na₂SO₄, Na₂SO₃, KH₂PO₄ and KBr; (f) Pb(NO₃)₂ and NaNO₂; (g) FeCl₃; and(h) FeCl₃ (after sample treatment with a strong base to selectivelyremove Fe³⁺). As shown in FIG. 9, only samples containing Cr⁶⁺ inducedsignificant optical changes (ΔA≧60%) after a 1-min exposure time.Furthermore, the selectivity of Cr⁶⁺ over Fe³⁺ was remarkable.

Whereas the 10-based sensor did not respond to Cr⁶⁺ in the absence ofH⁺, as shown above, it was capable of optically sensing Fe³⁺ in H₂O andMeCN, under neutral conditions, as we have previously described (Guptaand van der Boom, 2007). Apparently, this dual sensor system was capableof detecting a specific metal ion by varying the pH. Time-dependentmeasurement of the oxidation of the 10-based monolayer by aqueoussolutions containing 80 ppm Fe³⁺ or Cr⁶⁺ showed that the opticalresponse of the sensor towards the latter ion was at least 6 timesgreater within 1-min of exposure time, as shown in FIG. 10. Moreover,Fe³⁺ could selectively be removed from the medium by treatment with astrong base, as described in Materials and Methods, prior to analysis ofthe Cr⁶⁺ content by the 10-based monolayer (FIG. 9, entry h). Cr⁶⁺ isstable under basic conditions (Ji et al., 2001).

Example 7 Compound 10 Optically Recognizes Cr⁶⁺ in Environmental Samples

The formation of device quality sensors requires not only the ability todetect analytes under controlled laboratory conditions, but also underenvironmental conditions. Indeed, the 10-based monolayer has also beenused to detect Cr⁶⁺ in environmental samples. Water from a fishing pondand playground sand samples were collected and analyzed with and withoutthe addition of ppm-levels of Cr⁶⁺, as described in Materials andMethods. The Cr⁶⁺ was extracted from the sand with water. All watersamples were acidified to pH=1. As shown in FIG. 11, only samplescontaminated with Cr⁶⁺ gave positive responses.

Example 8 The 10-Based Monolayer is Stable Under Acidic Conditions

Since compound 10 was found to be highly selective to Cr⁶⁺ in thepresence of H⁺ only, stability of the 10-based monolayer towards acidicconditions is preferable. In order to evaluate its stability under saidconditions, the 10-based monolayer was immersed in water at pH 1 forseveral hours, the substrate was gently wiped with task paper and dried,and the absorption of MLCT bands at λ=516 and 692 were then recorded. Asshown in FIG. 12, the 10-based monolayer was stable for at least 12hours in an acidic environment; however, over a longer extended periodof time (56 h), a decrease of 18% in the absorption of both MLCT bandswas observed (data not shown). Nevertheless, comparing the stability atpH 1 for several hours with a 1 min response time of the 10-basedmonolayer in most experiments, it can be concluded that this monolayeris stable under conditions required for detection and quantification ofCr⁶⁺. At high pH (>9), however, removal of the 10-based monolayer fromthe glass substrates was observed by hydrolysis of the Si—O bond, whichis in good agreement with Wasserman et al. (1989).

Example 9 The 10-Based Monolayer may be Used for Cr⁶⁺ CatalyticDetoxification

As shown in the preceeding Examples, the Cr⁶⁺ detection method is redoxcoupled, i.e., associated with the oxidation of the 10-based monolayerfrom Os²⁺ to Os³⁺, followed by Cr³⁺ generation as indicated by ESR. Aswas further shown, the oxidation of the Os metal center may bereversibly switched in solution, depending of the pH, as indicated byUV/visible spectra, with subsequent Cr³⁺ formation.

In a typical experiment, 1 mM K₂Cr₂O₇ (2 times excess) was reacted with3 mM [Os(bpy)₃]Cl₂, and the pH of the obtained solution was modulatedbetween pH 1-12, using 10 M HCl and 10 M KOH. After each addition ofbase/acid, the pH was measured and the solution was allowed to stir foradditional 5 min. Upon acidification of the solution to pH 1, a fastcolor change was observed from dark green, indicating Os²⁺, to red,indicating oxidation of the Os²⁺ (as Os³⁺ has no color, the red colorwas probably due to other interactions); however, when the solution wasmade basic, the reverse color change was observed from red to dark green(data not shown). These oxidation/reduction cycles were repeated (×8)until no color change was observed, and the final solution (pH 1) wasanalyzed for Cr⁶⁺ using the 10-based monolayer. The monolayer wasimmersed for 6 min in the solution, at pH 1, during which the UV/visiblespectrum was recorded with 1 min intervals, and as shown in FIG. 13, theamount of Cr⁶⁺ detected by the 10-based monolayer after a 6 min exposurewas ˜>1 ppm (hence the 9% response of 1 ppm after 1 min) vs. 60 ppm inthe original solution, indicating that switching of the oxidation stateof the Os metal center may be done until the Cr⁶⁺ amount is fullyconsumed. The solution was also analyzed by ESR for the presence ofCr³⁺, and as shown in FIG. 14, Cr³⁺ was indeed formed after the“catalytic” treatment of the initial 1 mM K₂Cr₂O₇ solution. FIG. 15shows the oxidation of the 10-based monolayer by Cr⁶⁺ and the resettingby H₂O, as a function of the pH, indicating that the optimum pH valuefor the catalytic reaction described above is probably between pH1.5-3.0.

In view of the experimental data described hereinabove, it is concludedthat chemically surface bound 10-based monolayers may effectively beapplied in a reactor for Cr⁶⁺ waste water treatment. A graphical drawingof such a reactor, in which Cr⁶⁺ waste water are catalytically detoxifywith glass beads functionalized with 10-based monolayers, is shown inFIG. 16.

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1. A hexavalent chromium (Cr⁶⁺) sensor device comprising a divalentosmium (Os²⁺)-, iron (Fe²⁺)- or ruthenium (Ru²⁺)-based pyridyl complexcapable of changing its oxidation state in response to a reduction ofCr⁶⁺ at the presence of H⁺, thereby causing a reversible and opticallyreadable change in optical properties of said complex.
 2. The device ofclaim 1, comprising Os²⁺-based pyridyl complex.
 3. The device of claim1, wherein said pyridyl complex is charged tris-bipyridyl Os²⁺, Fe₂ ⁺ orRu₂ ⁺ complex or a derivative thereof.
 4. The device of claim 3, whereinsaid pyridyl complex is a compound of the general formula I:

wherein M is Os, Fe or Ru; n is the formal oxidation state of theosmium, iron or ruthenium, wherein n is 2 or 3; m is the positive chargeof the tris-bipyridyl ligand, wherein m is an integer from 0 to 24, X isa counter anion selected from Br⁻, Cl⁻, F⁻, I⁻, PF₆ ⁻, BF₄ ⁻, OH⁻, ClO₄⁻, SO₃ ⁻, CF₃COO⁻, CN⁻, alkylCOO⁻, arylCOO⁻ or a combination thereof;and R₅ to R₂₈ is each independently selected from hydrogen, halogen,hydroxyl, azido, nitro, cyano, amino, substituted amino, thiol, C₁-C₁₀alkyl, cycloalkyl, heterocycloalkyl, haloalkyl, aryl, heteroaryl,alkoxy, alkenyl, alkynyl, carboxamido, substituted carboxamido,carboxyl, protected carboxyl, protected amino, sulfonyl, substitutedaryl, substituted cycloalkyl or substituted heterocycloalkyl, wherein atleast one of said R₅ to R₂₈ is a group A or B:

wherein A is linked to the ring structure of the compound of generalformula I via R₄; R₄ is selected from cis/trans C═C, C≡C, N═N, C═N, N═C,C—N, N—C, alkylene, arylene or a combination thereof; R₃ is C or N; R₂is absent or is selected from hydrogen, alkyl, alkylene, aryl, arylene,OH, O-alkyl, O-alkylene or a combination thereof; and R₁ is absent or isselected from hydrogen, trialkoxysilane, trihalidesilane, thiol, COOH,COO⁻, Si(OH)₃ or phosphonate; and B is —O(CH₂)_(p)—R₂₉ linked to thering structure of the compound of general formula I via the oxygen,wherein p is an integer from 9 to 12; and R₂₉ is selected from hydrogen,trialkoxysilane, trihalidesilane, thiol, COOH, COO⁻, Si(OH)₃ orphosphonate; and any two vicinal R₅-R₂₈ substituents, together with thecarbon atoms to which they are attached, may form a fused ring systemselected from cycloalkyl, heterocycloalkyl, heteroaryl or aryl, whereinsaid fused system may be substituted by one or more groups selected fromC₁-C₁₀ alkyl, aryl, azido, cycloalkyl, halogen, heterocycloalkyl,alkoxy, hydroxyl, haloalkyl, heteroaryl, alkenyl, alkynyl, nitro, cyano,amino, substituted amino, carboxamido, substituted carboxamido,carboxyl, protected carboxyl, protected amino, thiol, sulfonyl orsubstituted aryl; and said fused ring system may also contain at leastone heteroatom selected from N, O or S.
 5. The device of claim 4,wherein said pyridyl complex is the compound of the general formula I,wherein: (i) M is Os, Fe or Ru, n is 2, m is 0, X is PF₆ ⁻ or I⁻, R₅, R₇to R₂₆ and R₂₈ each is hydrogen, R₆ is methyl, and R₂₇ is A, wherein R₄is C═C, R₃ is N, and R₂ and R₁ are both absent (compounds 4a-4-b, 5a-5band 6a-6b, respectively);

(ii) M is Os, Fe or Ru, n is 2, m is 1, X is PF₆ ⁻ or I⁻, R₅, R₇ to R₂₆and R₂₈ each is hydrogen, R₆ is methyl, and R₂₇ is A, wherein R₄ is C═C,R₃ is N, R₂ is methyl, and R₁ is absent (compounds 7a-7b, 8a-8b and9a-9b, respectively);

(iii) M is Os, n is 2, m is 1, X is PF₆ ⁻ or I⁻, R₅, R₇ to R₂₆ and R₂₈each is hydrogen, R₆ is methyl, and R₂₇ is A, wherein R₄ is C═C, R₃ isN, R₂ is propyl, and R₁ is trimethoxysilane (compounds 10a and 10b,respectively);

(iv) M is Os, Fe or Ru, n is 2, m is 0, X is PF₆ ⁻ or I⁻, R₅, R₇ to R₂₆and R₂₈ each is hydrogen, R₆ is methyl, and R₂₇ is A, wherein R₄ is C═C,R₃ is C, R₂ is OH, and R₁ is absent (compounds 11a-11b, 12a-12b and13a-13b, respectively);

(v) M is Os, n is 2, m is 0, X is PF₆ ⁻ or I⁻, R₅, R₇ to R₂₆ and R₂₈each is hydrogen, R₆ is methyl, and R₂₇ is A, wherein R₄ is C═C, R₃ isC, R₂ is O-propyl, and R₁ is trimethoxysilane (compounds 14a and 14b,respectively); or

(vi) M is Os, n is 2, m is 0, X is PF₆ ⁻ or I⁻, R₅, R₇ to R₂₆ and R₂₈each is hydrogen, R₆ and R₂₇ each is B, wherein p is 9 and R₂₉ istriethoxysilane (compounds 15a and 15b, respectively).

6-10. (canceled)
 11. The device of claim 1, wherein said opticalproperties are optical absorption spectra of said pyridyl complex at theUV/visible spectral range, preferably at the range of 400-900 nm. 12.The device of claim 2, further capable of changing its oxidation statein response to a reduction of Fe³⁺ at neutral pH, for detection of Fe³⁺.13. The device of claim 1, further comprising a substrate carrying alayered structure of said pyridyl complex.
 14. The device of claim 13,wherein: (i) said layered structure comprises a monolayer of saidpyridyl complex, or a plurality of identical or different layers of saidpyridyl complex; (ii) said pyridyl complex is bound to a linker designedto covalently bind to the surface of said substrate; or (iii) thesurface of said substrate carries a functional group capable ofcoordinating or binding to said layered structure. 15-16. (canceled) 17.The device of claim 14, wherein said functional group is capable ofeither covalently or non-covalently binding to said layered structure.18. The device of claim 13, wherein: (i) said substrate is hydrophilic,hydrophobic or a combination thereof; (ii) said substrate includes amaterial selected from glass, a doped glass, indium tin oxide(ITO)-coated glass, silicon, a doped silicon, Si(100), Si(111), SiO₂,SiH, silicon carbide mirror, quartz, a metal, metal oxide, a mixture ofmetal and metal oxide, group IV elements, mica, a polymer such aspolyacrylamide and polystyrene, a plastic, a zeolite, a clay, wood, amembrane, an optical fiber, a ceramic, a metalized ceramic, an alumina,an electrically-conductive material, a semiconductor, steel or astainless steel; or (iii) said substrate is optically transparent to theUV and visible spectral ranges.
 19. (canceled)
 20. The device of claim18(ii), wherein said substrate is in the form of beads, microparticles,nanoparticles, quantum dots or nanotubes.
 21. (canceled)
 22. The deviceof claim 13, wherein said substrate is glass, preferably glass slides orbeads, said pyridyl complex is the compound of the general formula Iwherein M is Os, n is 2, m is 1, X is PF₆ ⁻ or I⁻, R₅, R₇ to R₂₆ and R₂₈each is hydrogen, R₆ is methyl, and R₂₇ is A, wherein R₄ is C═C, R₃ isN, R₂ is propyl, and R₁ is trimethoxysilane (compounds 10a and 10b,respectively), and a monolayer of said pyridyl complex is covalentlybound to said substrate.
 23. An acidic aqueous solution comprising adivalent osmium (Os²⁺)-, iron (Fe^(2±))- or ruthenium (Ru²⁺)-basedpyridyl complex capable of changing its oxidation state in response to areduction of Cr⁶⁺ at the presence of H⁺, for selective detection andquantification of Cr⁶⁺.
 24. The solution of claim 23, comprisingOs²⁺-based pyridyl complex.
 25. The solution of claim 24, having a pH ata range of 0.1-3, preferably 0.3-2, most preferably about
 1. 26. Anampoule containing an acidic aqueous solution according to claim
 23. 27.A kit containing at least two ampoules according to claim
 26. 28. Amethod for selective detection and quantification of Cr⁶⁺ in a liquidsample, comprising: (i) exposing a divalent osmium (Os²⁺)-, iron (Fe²⁺)-or ruthenium (Ru²⁺)-based pyridyl complex capable of changing itsoxidation state in response to a reduction of Cr⁶⁺ to said sample, for asufficient time period at the presence of H⁺; (ii) recording absorptionspectra of said pyridyl complex at the UV/visible spectral range,preferably at the range of 400-900 nm; and (iii) monitoring the presenceof Cr⁶⁺ in said sample and determining its concentration according tothe change in the absorption spectra of (ii) compared to a predeterminedabsorption spectra of said pyridyl complex.
 29. The method of claim 28,wherein said pyridyl complex is carried as a layered structure on asubstrate, or wherein said liquid sample is obtained as a result oftreating a solid sample by a liquid media.
 30. (canceled)
 31. The methodof claim 28, wherein said pyridyl complex is Os²⁺-based pyridyl complex.32. The method of claim 31, wherein: (i) a decrease of the metal toligand charge transfer (MLCT) bands at λ=516 and 692 nm indicates thepresence of Cr⁶⁺, and the percentage of said decrease is proportional tothe concentration of Cr⁶⁺ in said sample; or (ii) said Os²⁺-basedpyridyl complex is exposed to said sample at a pH in a range of 0.1-3,preferably 0.3-2, most preferably about 1, and said sufficient timeperiod is about 1 min.
 33. (canceled)
 34. A method for detoxification ofCr⁶⁺ in an aqueous or organic liquid media, comprising: (i) contactingsaid liquid media with a divalent osmium (Os²⁺)-, iron (Fe²⁺)- orruthenium (Ru²⁺)-based pyridyl complex capable of changing its oxidationstate to Os³⁺-, Fe₃ ⁺- or Ru₃ ⁺-based pyridyl complex, respectively, inresponse to a reduction of Cr⁶⁺, for a sufficient time period at thepresence of H⁺, wherein said pyridyl complex is carried as a layeredstructure on a substrate; (ii) monitoring the presence of Cr⁶⁺ anddetermining its concentration in a sample taken from said liquid media;and (iii) when Cr⁶⁺ is detected in said sample, reducing said Os³⁺-,Fe³⁺- or Ru³⁺-based pyridyl complex and repeating steps (i) and (ii).35. The method of claim 34, wherein said substrate is in the form ofbeads, nanoparticles, quantum dots or nanotubes; or the monitoring ofthe presence of Cr⁶⁺ and the determination of its concentration in step(ii) is carried out by flame atomic absorption spectrometry (FAAS),inductively coupled plasma atomic emission spectrometry (ICP-AES),chemiluminescence, X-ray fluorescence, electrochemical methods or by themethod of claim
 29. 36. (canceled)
 37. The method of claim 34, whereinsaid pyridyl complex is Os²⁺-based pyridyl complex.
 38. The method ofclaim 37, wherein said Os²⁺-based pyridyl complex is contacted with saidliquid media at a pH in a range of 0.1-3, preferably 0.3-2, mostpreferably about
 1. 39. A method for detoxification of Cr⁶⁺ in anaqueous or organic liquid media, comprising contacting said liquid mediawith a divalent osmium (Os²⁺)-, iron (Fe₂ ⁺)- or ruthenium (Ru₂ ⁺)-basedpyridyl complex capable of changing its oxidation state to Os³⁺-, Fe³⁺-or Ru³⁺-based pyridyl complex, respectively, in response to a reductionof Cr⁶⁺, for a sufficient time period at the presence of H⁺, whereinsaid pyridyl complex is carried as a layered structure on a substrate.40. A catalytic process for reduction of Cr⁶⁺, comprising reducing saidCr⁶⁺ with a divalent osmium (Os²⁺)-based pyridyl complex to therebyoxidize the Os²⁺ to Os³⁺, and exposing the oxidized Os³⁺ to water for asufficient time period to thereby regenerate the Os³⁺ to Os²⁺.